1. 3D text

Use the Type tool, type in "3D Logo". Go to Effect >Warp > Arc and apply the following setting:

2. 3D Extrude & Bevel

Then go to Effect > 3D > Extrude & Bevel and apply the setting as shown in the image below. You can drag around the cube to set the X,Y,Z rotation values. Set the Extrude Depth to 20pt.

3. Expand Appearance

Now go to Object > Expand Appearance to remove all effects and convert to paths. After the text object is expanded, Ungrounp the object by Object > Ungroup or press Ctrl+Shift+G. You probably need to do Ungroup 4-5 times in order to break the object apart.

4. Merge paths

Select the round corner paths and merge them together by the Pathfinder tool. Hold down Alt key, click on the Add to shape area and the selected paths will be merged. Repeat this step to clean up all round corner paths.

5. Apply gradient

Select the top level paths and apply a yellow-green color gradient.

6. Eyedropper

Select the back(depth) paths, use the Eyedropper tool and click on the front paths. This will copy the gradient fill.

7. Darken

Keep the back paths selected, go to Gradient pallete and adjust the gradient colors to darker tone.

8. 3D logo

You can use this technique to make 3D objects from any shape, text, etc.